A substrate processing apparatus for performing a plasma process, e.g., an etching process, on a wafer as a substrate includes an accommodation vessel (chamber) for accommodating the wafer and a substrate mounting table, disposed in the chamber, for mounting the wafer thereon. The substrate processing apparatus generates a plasma in the chamber and performs an etching process on the wafer mounted on the substrate mounting table by the plasma.
The substrate mounting table is provided with an electrostatic chuck made of an insulating member, e.g., ceramic, and an electrostatic electrode plate is provided in the electrostatic chuck. A DC voltage is applied to the electrostatic electrode plate while an etching process is performed on the wafer, so that the wafer is attracted and held on the electrostatic chuck by Coulomb force or Johnsen-Rahbek force generated by the DC voltage.
FIG. 5 is a cross sectional view schematically showing a configuration of a substrate mounting table of a conventional substrate processing apparatus.
The substrate mounting table 70 mainly includes a base portion 71 formed of, e.g., aluminum, an electrostatic chuck (ESC) 72 disposed on an upper planar surface of the base portion 71, an adhesive layer 73 for adhering the electrostatic chuck 72 to the base portion 71, and a focus ring 75 arranged to surround the electrostatic chuck 72. A circular wafer W is mounted on an upper planar surface of the electrostatic chuck 72.
A thermally sprayed film is formed on the upper planar surface of the base portion 71 by spraying ceramic made of, e.g., alumina, yttrium or the like in order to insulate the base portion 71. Further, since it is necessary to clean the inside of the chamber by using the plasma, plasma resistance and pressure resistance are required in the electrostatic chuck 72. Thus, recently, an integrated plate chuck is preferably used as the electrostatic chuck 72. The electrostatic chuck 72 serving as a plate chuck is formed of ceramic having a thickness of about 1 mm, and an electrostatic electrode plate 74 is embedded in the electrostatic chuck 72.
The focus ring 75 is formed of, e.g., single crystalline silicon and mounted at an outer peripheral portion of the upper planar surface of the base portion 71 to surround the wafer W mounted on the electrostatic chuck 72. The focus ring 75 makes the plasma density above a peripheral portion of the wafer W substantially equal to the plasma density above a central portion of the wafer W by extending a plasma distribution region to an upper region above the focus ring 75 as well as an upper region above the wafer W. Accordingly, it is possible to maintain uniformity of an etching process being performed on the entire surface of the wafer W.
There is a gap between the electrostatic chuck 72 and the focus ring 75 in the conventional substrate mounting table. The plasma enters into the gap and a gap between the wafer W and the focus ring 75. Accordingly, there is a problem in which the adhesive layer 73 formed of an organic material is worn by irradiation of the plasma. Further, a surface 71a of the base portion 71 between the electrostatic chuck 72 and the focus ring 75 is exposed. The plasma is irradiated on the exposed surface 71a and the thermally sprayed film is worn. Then, when the aluminum of the base portion 71 is exposed, abnormal discharge (arcing) may occur. The wear of the adhesive layer 73 and the occurrence of the abnormal discharge exert a bad influence on the functions of the substrate mounting table, thereby shortening a life span of the substrate mounting table.
Accordingly, it is required to develop a substrate mounting table capable of avoiding the wear of the adhesive layer for adhering the electrostatic chuck to the base portion. There is proposed a substrate mounting table configured to cover a peripheral portion of the adhesive layer with a protective coating (see, e.g., Japanese Patent Application Publication No. 2000-286332).
However, in the substrate mounting table disclosed in Japanese Patent Application Publication No. 2000-286332, not only the adhesion portion between the electrostatic chuck main body and the base portion but also the entire electrostatic chuck main body and a part of the base portion are coated with a fluorine resin protective film as a separate member. Accordingly, the fluorine resin protective film is added as a new constituent component and there is a problem of increasing the number of components and the number of assembly steps.